This spring body is manufactured from a cubical piece and is divided into an upper and a lower guide bar by a horizontal opening extending all the way through it, so that the spring body also forms the parallel guide for the balance scale and has wire strain gauges or the equivalent at thin spots in the area of at least one of the guide bars. Spring bodies of this type are generally known and are described, for example, in Swiss Pat. No. 353,555 by FIGS. 4 and 5 or in German Federal Republic DE Pat. No. 2,900,614 by FIGS. 1 and 2.
A disadvantage of these known structures is the fact that when there is an off-center load on the balance scale in a direction vertical to the longitudinal plane of the spring body, very great bending and torsional moments act on the guide bars. This limits the possible size of the scale and furthermore leads to large expansion gradients in the area of the strain gauges, thus making necessary a very exact positioning of the strain gauges.